This invention relates to a method for the preparation of silicone-containing copolycarbonates. More particularly the method relates to a method for obtaining silicone-containing copolycarbonates which are transparent.
Silicone-containing copolycarbonates are prized for their unique combination of ductility, toughness, and flame retardance. Silicone copolycarbonates are typically prepared by reaction of a mixture of a siloxane-containing bisphenol and a bisphenol such as bisphenol A under interfacial conditions with phosgene and an aqueous acid acceptor such as sodium hydroxide in water. Alternatively, siloxane-containing copolycarbonates may be prepared by reaction of a chloroformate-terminated polycarbonate oligomer with a siloxane-containing bisphenol. Typically, the reaction between the chloroformate-terminated polycarbonate oligomer and the siloxane-containing bisphenol is carried out under interfacial conditions similar to those employed when a bisphenol and a siloxane-containing bisphenol are copolymerized directly with phosgene. Such approaches to silicone-containing copolycarbonates are illustrated in Japanese Patent Application JP 9265663, European Patent Application EP 500131, U.S. Pat. No. 5,530,083, U.S. Pat. No. 5,502,134, and copending U.S. patent application Ser. No. 09/613,040.
In copending U.S. patent application Ser. 09/613,040 a group of silicone-containing copolycarbonates is disclosed which are substantially single phase and transparent. However, transparent silicone-containing copolycarbonates could be obtained only when siloxane chain lengths were short (less than about 20 Me2SiO units). It would be economically advantageous to produce transparent silicone-containing copolycarbonates having relatively long siloxane chain lengths. The present invention provides a method for the preparation of silicone-containing copolycarbonates which remain transparent even when the siloxane chain lengths are relatively long.
In one aspect, the present invention provides a method of preparing silicone-containing copolycarbonate compositions, said method comprising:
Step (a) contacting a hydroxy-terminated polycarbonate oligomer with a siloxane bischloroformate under interfacial reaction conditions to afford a silicone-containing polycarbonate intermediate;
Step (b) reacting said intermediate under interfacial reaction conditions with at least one bisphenol, at least one endcapping agent, and phosgene to provide a silicone-containing copolycarbonate.
In another aspect, the present invention relates to the silicone-containing copolycarbonate compositions prepared by the method of the present invention. In yet another aspect, the present invention relates to silicone-containing polycarbonate intermediates useful in materials synthesis.